The present invention relates generally to heating devices and resettable fuses, and more particularly to heaters which are flexible and fuse devices which use positive temperature coefficient (PTC), negative temperature coefficient (NTC) material, and/or Voltage Sensitive Material (VSM) to provide current and voltage protection for a circuit or device.
There have been prior attempts to make flexible self-regulating heating elements. U.S. Pat. No. 4,668,857 to Smuckler, U.S. Pat. No. 4,503,322 to Kisimoto, U.S. Pat. No. 5,558,794 to Jansens, U.S. Pat. No. 4,742,212 to Ishi, U.S. Pat. No. 4,661,690 to Yamamoto and U.S. Pat. No. 4,200,973 to Farkas disclose various types of heaters in the form of cables. Some, such as the embodiment pictured in FIG. 1 of Smuckler have a side-by-side construction which will not be equally flexible in all directions. Additionally, the heaters which use PTC materials as a self-regulating device, generally must be designed differently to work with 120 volt line voltages than with 240 volt line voltages. There is a need for a heater cable which can be used with both such power supplies.
Self regulating heaters have also been formed into sheets in such patents as U.S. Pat. No. 4,777,351 to Batliwalla, U.S. Pat. No. 4,700,054 to Triplett, and U.S. Pat. No. 5,422,462 to Kishimoto. In these patents, the heating elements are configured as sheets, or as fabrics, which have interdigitized or interleaved electrodes between which elements of PTC are positioned. This allows the use generally of a limited range of voltages, generally 120 Volts, and thus a limited amount of heat production. There are some heaters which may operate at as much as 480 Volts, these are generally three input, three phase systems, but to the inventor""s knowledge, there is no heater system which can be operated at 480 Volts with a two input bus system.
There are many applications in which it is desirable to wrap irregular objects, such as pipeline valves with heating devices. Many of these applications also require much flexibility in the amount and shape of the heater material used. For this reason, it is highly desirable that self-regulating heaters be modular in design, so that specific lengths of heater material may be joined together to make greater lengths, and also desirable that the lengths be capable of being trimmed to shorter lengths, without of course losing power or heating capacity. Of course, the most preferred example of this flexibility in length choice would be if the material is capable of being trimmed to any length within a modular section, that is, it is continuously variable. Next best is a material which contains certain defined zones for the heating elements, and the material may be trimmed in between any of these heating zones. This allows the length to be varied in multiples of these zone lengths, and these can be referred to as incrementally variable in length.
There have been several attempts at creating modular heaters which are self-regulating. U.S. Pat. No. 4,638,150 to Whitney, and U.S. Pat. No. 4,072,848 to Johnson show heaters which have self-regulating elements and which may be considered modular. These heating modules are generally rigid, and if they are trimmable at all, they would certainly be only incrementally variable. As the elements are generally not flexible, their application is thus expected to be limited.
PTC elements have also been used as resettable fuses in U.S. Pat. Nos. 5,796,569, and 5,818,676 to Gronowicsz, U.S. Pat. No. 5,682,130 to Styrna, U.S. Pat. No. 5,801,914 to Thrash, and U.S. Pat. No. 5,495,383 to Yoshioka. These fuses will protect the circuit from current which is too high, but will provide little protection for voltage spikes, for which the response time of PTC may be too slow. Thus there is a need for a resettable fuse which can protect a circuit from voltage spikes.
Accordingly, it is an object of the present invention to provide modular or long length heaters which are flexible to conform to shapes of irregular objects and can be made to wrap around pipes.
Another object of the invention is to provide modular heaters which can connectable to any length or interconnected.
And, another object of the invention is to provide low voltage heaters which operate in the range of 0.1-12 volts.
A further object of the invention is to provide high voltage heaters which operate over 240 volts.
A yet further object of the present invention is to provide heaters which are either self-limiting, or which provide built-in safety protection.
Briefly, a preferred embodiment of the present invention is a self-regulating heating device for operation with supply voltages in the range of 0.1-12 volts having first and second layers of material, at least one of which is PTC material interposed between a first electrode and a second electrode.
Another preferred embodiment is a self-regulating heating device for operation with supply voltages above 240 volts having first and second layers of material, at least one of which is PTC material interposed between a first electrode and a second electrode.
An advantage of the present self-regulating modular heater is that it is very flexible, can fit around irregular fittings and valves, can be attached together in modular lengths and can be cut to almost any desired length.
Another advantage of the present self-regulating modular heater is that they also are very flexible, can wrap around small diameter pipes, and can also be used with low voltage power supplies in the range of 0.1-12 volts AC or DC, so that they can be powered, for instance, by batteries.
A further advantage of the present self-regulating modular heater is that they can be used at high voltages above 240 volts.
These and other objects and advantages of the present invention will become clear to those skilled in the art in view of the description of the best presently known mode of carrying out the invention and the industrial applicability of the preferred embodiment as described herein and as illustrated in the several figures of the drawings.